Adult rat myoblast culture and immunolabelling from the courtesy of Juliette Peltzer and Dr Angelica Keller, image acquisition and processing from Gilles Carpentier, Faculte des Sciences et Technologies, Universite Paris 12-Val de Marne, France. Images were acquired with a BH2 Olympus microscope in epifluorescence mode (oil immersion objective 100 x), with a CFW1310 monochrome IEEE camera. Computer acquisition and processing were performed on a Macintosh G4 eMac, upon MacOS X3 operating system. Acquisition thru Scion ImageJ version software. Image processing by public domain Image 1.34 software, available for Windows & Mac OS, Mac OS X and Linux, developped by Wayne Rasband (wayne@codon.nih.gov), at the Research Services Branch, National Institute of Mental Health, Bethesda, Maryland, USA (http://rsb.info.nih.gov/ij/). Acquisition parameters: Red channel: "Texas red" labelling fluorescence; 1200 ms, 10 bit mode, 2 image average. Image treatment: (normalized histogram (16 bit encoded)) Green channel : FITC labelling fluorescence. 2800 ms, 10 bit mode, 2 image average Image treatment: gamma function (0.6) following by a normalisation of histogram (16 bit encoded) RGV composite obtained with the ImageJ 24 bit color merge function .